A normal procedure for non-destructive materials testing with ultrasound (US) consists of one or more ultrasonic transducers being moved past the contour of a test object, whereby a map of the test object is created with any faults that may have been found.
Ultrasonic transducers in such cases are located in a positioning system which is usually moved by servo motors. Their operating currents are adjusted by converters using pulse width modulation (PWM). The destination points for outputting the pulses and the evaluation of the incoming echoes are controlled by the positioning system in order to obtain the assignment of the signals to the measurement location.
While the signal voltage of the ultrasonic transducer, triggered by the ultrasonic echo only amounts to a few mV, the operating voltages and currents of the servomotors can amount to a few hundred volts and a few amperes. The pulse width modulation of these voltages and currents produces steep switching edges on the motor lines, which can couple into the signal circuit of ultrasonic transducers by electromagnetic coupling. Thus undesired interference voltages of the same order of magnitude as the desired signal voltages can be generated and the measurement result corrupted by said interference. This situation can be seen in FIG. 4.
To find material faults with a different orientation to the surface, one and the same point on the surface is tested frequently by different ultrasonic transducers with different angles of incidence. The sequential activation of the individual transducers significantly lengthens the testing time.